1. Field of the Invention
This invention relates to an artificial intervertebral prosthesis. More particularly, the present invention relates to a stable, yet flexible, synthetic intervertebral disk prosthesis for insertion into a spine following removal of a natural disk.
2. Description of the Related Art
The spine is a flexible structure comprised of thirty-three vertebrae. The vertebrae are separated and cushioned from each other by fibro-cartilaginous structures called the intervertebral disks. If the spine is injured or becomes diseased, these disks may be surgically removed.
The present treatment of lumbar disk herniation is a compromised functional recovery at best. The disk that has come out of its place has no physiological function and at this time no method is known that will bring back the functional lumbar disk. A disk prosthesis is needed which can be applied to the disk space and provide the cushioning effect for the disk that is expected of the normal disk.
Several unacceptable attempts have been made to solve these problems; such as applying spring loaded disk prosthesis or saline injectable disks with suction cups on the surfaces. The spring loaded disk is so bulky it cannot be inserted into the disk space through the limited opening that is available for this kind of surgery. The saline injectable disk is unstable and the suction cups do not hold it onto the vertebral bodies with their irregular spikey surfaces.
Various methods have been employed to deal with the problems that occur after disk removal. One common procedure has been, after disk removal, to fuse the vertebrae that were previously separated from the disk. Unfortunately, this procedure virtually precludes any degree of spinal flexibility. Similarly, disk removal has been followed by replacement with a disk prosthesis purportedly designed to replicate a natural disk's function. However, although artificial disk prostheses have been developed, none are completely satisfactory.
U.S. Pat. No. 4,309,777 to Patil discloses an artificial disk having a plurality of springs positioned between lower and upper disk portions. In addition, a plurality of spikes extend from the upper and lower portions of the disk to engage the vertebrae. U.S. Pat. No. 4,759,769 to Hedman discloses an artificial spinal disk comprised of upper and lower portions connected by both hinge and spring devices. The Patil and Hedman disks, albeit stable, lack a physiological structure and therefore are not used. U.S. Pat. No. 4,834,757 to Bramtigan discloses vertebral implant plugs on blocks useful in fusing together adjoining vertebral bodies. U.S. Pat. No. 4,863,476 to Sheppard discloses an elongated spinal implant intended for insertion in an intervertebral space. However, the Sheppard implant lacks the advantage of maintaining full contact with the vertebrae. U.S. Pat. No. 4,863,477 to Monson discloses a synthetic intervertebral disk prosthesis composed of a rubber-type material having a hollow interior. The interior may be filled with fluid imparting a certain degree of resiliency to the prosthesis. One disadvantage of the Monson prosthesis, however, is that in the anatomical context of the intervertebral space, its design provides very little stability. Thus, the need for a truly stable yet fully flexible artificial intervertebral disk prosthesis and implant exists and is now disclosed.